Directory of U.S. Military Rockets and Missiles|
Appendix 4: Undesignated Vehicles
|Copyright © 2004 Andreas Parsch|
Development of the D-21 Mach 3+ reconnaissance drone began in October 1962. The drone, then known by the Lockheed designation Q-12, was intended to supplement the CIA's A-12 aircraft for missions which required exceptionally long range and/or were too sensitive for the use of a manned aircraft. By October 1963, the Q-12's design had been finalized. It was to be an air-launched ramjet-powered vehicle using some key technology from the A-12 program like e.g. the titanium construction. The aircraft was to be launched from the back of a modified A-12 at a speed of Mach 3. Also in late 1963, the Q-12 was renamed D-21 and the carrier aircraft became the M-21 (M = "Mother", D = "Daughter") to prevent confusion from the proliferation of "-12" designations in the Blackbird family. The D-21 also received the project name Tagboard. It must be mentioned that Tagboard was a CIA program (although the USAF was of course deeply involved) and therefore the D-21 was - strictly speaking - not a military aircraft.
|Q-12/D-21 (full-scale mockup)|
The D-21 was powered by a single Marquardt RJ43-MA-11 ramjet, a modification of the engine used by the CIM-10 Bomarc missile. Its double-delta wing planform was similar to that of the A-12's outer wing sections. For launch, the M-21 accelerated to Mach 3+ at high altitude, the D-21's ramjet was ignited and the drone was released to free flight. This was a very risky manoeuver, because the clearance between the D-21's wings and the M-21's vertical tails was rather close, and the drone had to fly through the Mach 3 shockwave of the carrier aircraft. The D-21 had a nominal range of about 5550 km (3000 nm), was equipped with an inertial navigation system and the flight control computer could be pre-programmed with a course consisting of several waypoints. The drone's mission equipment was a single Hycon high-resolution photographic camera. At the end of the flight, the hatch with the camera was dropped over a pre-determined over-water area, where it could be retrieved by a mid-air recovery system. If that failed, the hatch was designed to float until recovered by a ship. The D-21 itself was expendable.
|D-21 (on M-21)|
Captive flight testing of the M-21/D-21 combination began in December 1964, and continued through 1965. In the first tests, the D-21 had aerodynamic covers over the intake and exhaust, but because the covers could not be dropped at Mach 3 without damaging the M-21 and/or D-21, they were deleted. The greater drag was overcome by using the D-21's ramjet as the third engine of the combination (the D-21's fuel tanks could be topped off from the M-21 before launch). The first actual launch of a D-21 finally occured on 5 March 1966, followed by two others on 27 April and 16 June that year. These were all moderately successful, but the fourth and final M-21/D-21 launch on 30 July ended in desaster. The D-21 hit the M-21's tail after separation, leading to the crash of both aircraft and the death of one of the two M-21 crewmembers. After this accident, the M-21/D-21 program was terminated.
Because the M-21/D-21 launch procedure was known to be risky, an alternative method had already been proposed before the ill-fated test. A slightly modified D-21 was to be launched from an underwing pylon on a B-52H. Because of the much slower release speed, the Tagboard drone would have to use a large solid-propellant rocket booster to accelerate it to ramjet ignition speed. The modified drone was designated D-21B (there was no -21A version), and all D-21s on order in mid-1966 were completed as D-21Bs. The two remaining original D-21s were also converted to this standard. Two B-52Hs were modified to launch the D-21B, and each of them could carry two drones. The D-21B had improved remote control and telemetry links, which would remain active up to 10 minutes into an operational mission.
Test launches of the D-21B ran from September 1967 to July 1969, and used up 12 Tagboard drones. However, the initial attempts were not very successful, and on the very first one the drone actually just fell off the pylon long before the B-52H had reached the launch area. But the last two test flights of the program were fully successful, ending with recovery of the hatch after the drone had covered more than 5370 km (2900 nm), and the B-52H/D-21B system was declared ready for operational missions.
A total of four operational missions were eventually flown (9 Nov 1969, 16 Dec 1970, 4 Mar 1971, 20 Mar 1971), all overflying the People's Republic of China under the project code name SENIOR BOWL. Only two (the 2nd and 3rd) drones completed their flights, but in both cases the hatch with the reconnaissance camera could not be recovered because of system malfunctions and/or bad handling of the recovery effort. In July 1971, the Tagboard program was cancelled. The reasons included the poor measure of success of the SENIOR BOWL flights, and the service entry of a new generation of photo reconnaissance satellites which could produce equivalent results without the political risks of flights through denied air space.
A total of 38 D-21/D-21B drones were built. 21 of these were expended in tests and operational missions, and the remaining 17 vehicles were placed in storage. In 1976/77, the Tagboard drones were moved to open storage at Davis-Monthan AFB. This was the first time that the general public learned about the existance of the vehicles. It was not before the early 1990s that the whole story of Tagboard and SENIOR BOWL was finally released. The D-21B drones in storage had been redesignated as GTD-21B. In standard aircraft designations, a "GT" prefix means "permanently grounded, used for training", but it is not known whether this is also valid for the Tagboard drone's final designation. Since the mid-1990s, the GTD-21Bs have been released to various museums.
Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!
Data for D-21B:
|Length (w/o booster)||13.06 m (42 ft 10 in); booster: 13.49 m (44 ft 3 in)|
|Wingspan||5.80 m (19 ft 0.25 in)|
|Height||2.14 m (7 ft 0.25 in)|
|Weight (w/o booster)||4990 kg (11000 lb); booster: 6027 kg (13286 lb)|
|Ceiling||29000 m (95000 ft)|
|Range||5550 km (3000 nm)|
|Propulsion||Marquardt RJ43-MA-11 ramjet; 6.7 kN (1500 lb)|
Booster: solid-propellant rocket; 121 kN (27300 lb) for 87 s
 Curtis Peebles: "Dark Eagles", Presidio Press, 1999
 Jay Miller: "Lockheed's Skunk Works", Midland Publishing, 1995
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